Reports of hair loss in bats in the wild are scarce and have not been summarized. We performed a literature review to summarize the affected species, prevalence, clinic diagnostics, and factors that cause alopecia in bats. We found only 28 studies that reported alopecia in 26 species of bats, within five families. Together, these studies examined 10,186 bats, of which 10.8% had alopecia, with a sex bias to females (3:1). Most studies did not identify a specific ethologic agent responsible for the hair loss. However, alopecia was attributed to five non-exclusive causes: endocrine factors related to reproduction and lactation, ectoparasites, the ingestion of toxins, and environmental stress. In the latter, anthropogenic stressors are of increasing concern — the incidence of alopecia in urban areas reflects reproductive stress, limited food availability, roost disturbance, and pollution in these poor-quality environments. Better reporting of alopecia in bats would help us better understand this pathology and to precisely measure environmental stress in these animals.